Spatial multiplexing communications system performance, including SDMA (space division, multiple access) and MIMO (multiple-input, multiple-output) systems, may be improved by the activities of training and calibration. Training may include transmitting known signals to a receiver to increase the reliability of estimating channel state information. While longer training sequences may provide increased reception accuracy, the use of such sequences may also reduce the advantage to be gained by using spatial multiplexing in the first place (i.e., high data rates). Similarly, while calibrating transmitter power and receiver gains can contribute to improved data transmission rates, the additional time required for periodic calibration may decrease the ultimate system capability to communicate large amounts of data in a short time span.